This removes "github.com/coreos/go-systemd/util", no longer needed after
removing the dependency on it.
It also gets rid of "github.com/coreos/pkg/dlopen", since that was only
referred to by the aforementioned "util" package.
Tested that everything builds and works as expected.
Signed-off-by: Filipe Brandenburger <filbranden@gmail.com>